The present invention relates to a method of manufacturing a semiconductor device, a molding device for a semiconductor device, and a semiconductor device.
A semiconductor device manufactured by securing a semiconductor chip to a die pad provided in a lead frame with an adhesive, connecting leads of the lead frame to electrodes of the semiconductor chip using gold wires to form a semiconductor assembly, placing the semiconductor assembly in a cavity, and curing a resin injected into the cavity so as to cover the semiconductor assembly has been known. FIG. 9 is a plan view showing part of such a semiconductor assembly.
In a semiconductor assembly 10 shown in FIG. 9, a semiconductor chip 12 is secured to a die pad 14 which has a square or rectangular shape. Suspension leads 16 are provided to connect four corners of the die pad 14 to a lead frame 18 and support the die pad 14. The lead frame 18 comprises a plurality of leads 20 between the suspension leads 16, and the leads 20 are connected to the terminals of the semiconductor chip 12 by wires (gold wires) 22.
This semiconductor assembly 10 is placed in a cavity with the leads 20 sandwiched between upper and lower molds and sealed with a resin injected into the cavity from a resin injection port of the mold which is provided at one corner of the die pad 14.
However, since the lead frame 18 supports the die pad 14 through the thin, narrow suspension leads 16, when the resin is injected into the cavity in which the semiconductor assembly 10 is placed, the semiconductor assembly 10 may tilt in a direction of the resin injection (in a direction along the axis of the resin injection port) or move up and down due to the flow of the injected resin in the cavity 24, as shown in FIG. 10. When manufacturing a semiconductor device having a total thickness xe2x80x9ctxe2x80x9d of 1 mm, 1.4 mm, or the like, the slight tilting or movement of the semiconductor assembly 10 may cause the die pad 14 or wires 22 to be in contact with the mold when the semiconductor assembly 10 is sealed, resulting in defective products in which the die pad 14 or wires 22 is exposed from the surface of the cured resin.
Therefore, conventional methods of eliminating such defects include a method of adjusting the height of the wires 22 in a wire bonding step in which the semiconductor chip 12 is connected to the leads 20 with the wires 22, or a method of changing molding conditions in the injection of the resin into the cavity 24. However, defective products with the die pad 14 or wires 22 exposed on the surface could not be eliminated due to fluctuation in processing or the like. Because the molding conditions have been adjusted based on the results of previous molding, countermeasures to a change in materials tend to delay and the degree of adjustment of the molding conditions tends to be too small to adequately remove the above defect.
The present invention has been achieved to solve the above problems of the prior art and has an objective of eliminating the defects in the molding step of resin sealing.
In order to achieve the above-described objective, a method of manufacturing a semiconductor device according to the present invention comprises a step of placing a semiconductor assembly in which a semiconductor chip is secured to a die pad of a lead frame in a cavity of a mold and sealing the semiconductor assembly with a resin injected into the cavity, wherein at least one support pin positioned substantially on the axis of a resin injection port of the mold is caused to come in contact with the semiconductor assembly, and wherein the resin injected into the cavity from the resin injection port is cured after the support pin has been pulled into the mold.
According to the present invention, the semiconductor assembly does not tilt or move due to the flow of the resin because the resin is injected while the semiconductor assembly is supported by the support pin. Therefore, the die pad or wires are not in contact with the mold, thereby eliminating defects such as exposure of the die pad or wires from the semiconductor assembly sealed with the resin. Moreover, since the support pins are pulled out of the mold cavity before the injected resin is cured, the semiconductor assembly is not exposed from holes which are formed in the points where the support pins have existed.
The semiconductor chip is not damaged if the support pin comes in contact with the die pad. The semiconductor assembly is supported more securely by arranging a plurality of support pins substantially on the axis of the resin injection port, thereby further reducing the tilting of the semiconductor assembly and the like. If pressure is applied to the semiconductor assembly by the support pins to move the assembly in a direction away from the previous position of the contact portion of the support pins, the support pins are pushed toward the mold by the semiconductor assembly due to the elasticity of the wires connecting the leads of the lead frame to the semiconductor chip and the suspension leads. Therefore, the semiconductor assembly is not lifted up by the resin even if the resin flows into the cavity under high pressure.
The semiconductor assembly may be placed in the cavity with the die pad either in the upper side or the lower side, depending on the client""s request. If the semiconductor assembly is placed with the die pad in the lower side, the support pin is preferably provided on the lower mold. If the semiconductor assembly is placed with the die pad in the upper side, the support pin is preferably provided on the upper mold. If the support pins are in contact with both the top and the bottom of the semiconductor assembly so as to sandwich the semiconductor assembly, the mispositioning of the semiconductor assembly can be more reliably prevented when injecting the resin. If a pair of support pins come in contact with the suspension leads which connect the die pad to the lead frame, the interval between the support pins becomes longer, whereby the semiconductor assembly can be securely supported.
In the method of manufacturing a semiconductor device according to the present invention, a heat radiator placed in a cavity of a mold is supported by at least one support pin provided substantially on the axis of a resin injection port; the mold is closed after a die pad of a lead frame to which a semiconductor chip is secured is placed on the heat radiator; and after the support pin is pulled into the mold, a resin injected into the cavity from the resin injection port is cured. According to the present invention, the heat radiator can be provided to the semiconductor assembly at the time of molding with the resin (sealing with the resin), thereby simplifying the manufacturing process.
If the heat radiator is supported by the support pin that is held by a recess formed on a lower surface of the heat radiator for preventing the heat radiator from moving, displacement of the heat radiator at the time of placing the semiconductor assembly on the heat radiator can be prevented, whereby the position of the semiconductor assembly on the heat radiator can be precisely determined. In this case, a plurality of support pins may be provided substantially on the axis of the resin injection port.
The molding device for carrying out the method of manufacturing the semiconductor device comprises: a mold which is capable of being opened or closed and is provided with a cavity for placing a semiconductor assembly which comprises a semiconductor chip secured to a die pad of a lead frame; a resin injection port provided to the mold for injecting a resin into the cavity; at least one support pin provided in the cavity substantially on the axis of the resin injection port such that the support pin is able to enter into or be pulled out of the cavity to come in contact with the semiconductor assembly in the cavity; and an actuator which moves the support pin in a direction of the axis of the support pin. Therefore, the semiconductor assembly does not tilt or move up and down, thereby eliminating defects such as exposure of the die pad or wires.
The semiconductor assembly can be securely prevented from tilting by providing a plurality of support pins substantially on the axis of the resin injection port. The support pins may be provided in either the upper mold or the lower mold as required. The support pins may be provided in both the upper and lower mold to sandwich the semiconductor assembly. Alternatively, the support pin may be provided at a position corresponding to the die pad so as to support the die pad. Instead, a pair of support pins may be provided substantially on the axis of the resin injection port, and the support pins may be placed at positions corresponding to suspension leads which connect the die pad of the semiconductor assembly placed in the cavity to the lead frame to support the suspension leads. If a servomotor is used as the actuator which moves the support pins in and out of the cavity, the vertical position of the support pin, the speed of pulling the support pin into the mold, operation mode, and the like can be optionally set. This ensures use of various types of molds with ease and prevents the formation of bubbles and the like in the resin at the time of pulling the support pin. A semiconductor device according to the present invention can be manufactured by the method of any one of Claims 1 to 11. Therefore, defective products such as one with an exposed die pad or wires can be eliminated.